JP2004083320A - Silicon single crystal growth method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon single crystal growth method using a CZ (Czochralski) method in which magnetic field application is performed for preventing the variation of crystal grain sizes in a drawing stage. <P>SOLUTION: A silicon raw material for crystals is charged into a crucible 1 and melted, and while rotating seed crystals 15 dipped into the melted liquid 13, the seed crystals 15 are pulled up, so that, through a drawing stage, a diameter increasing stage and a sizing stage, silicon single crystals 12 are grown in the lower direction of the seed crystals 15. In the drawing stage for removing dislocations, the speed of rotation in a crucible is controlled to ≤1 rpm, and a horizontal magnetic field of ≤0.1 T is applied to the melted liquid 13 by superconducting magnets 30a and 30b. The magnetic field application is stopped in a process where the drawing stage transits to the diameter increasing stage. The speed of rotation in the crucible is changed to ≥3 rpm in the process of the diameter increasing stage, and also, in the meantime for which the crystal grain size reaches 100 mm. <P>COPYRIGHT: (C)2004,JPO

Description

【００４０】
また、絞り工程で磁場を印加しても、その強度が０．１テスラを超える例えば０．３テスラの場合は、増径工程への移行時に磁場印加を停止したにもかわらず、結晶径が１００ｍｍに達するまでの間に有転位化が生じた。なお、ルツボ回転数は図２のパターンとした。
【００４１】
また、絞り工程で印加する磁場強度が０．１テスラ以下の例えば０．０５テスラであり、且つ増径工程への移行時に磁場印加を停止した場合であっても、絞り工程でのルツボ回転数が１ｒｐｍを超える例えば３ｒｐｍの場合は絞り工程における径変動が大きくなり、大重量結晶を保持することが困難となる。
【００４２】
また、絞り工程で印加する磁場強度が０．１テスラ以下の例えば０．０５テスラで、且つ絞り工程でのルツボ回転数が１．０ｒｐｍの場合であっても、増径工程で引き続き磁場印加を行った場合は増径工程の初期において有転位化が頻発した。なお、ルツボ回転数は図２のパターンとした。
【００４３】
【発明の効果】
以上に説明したとおり、本発明のシリコン単結晶成長方法は、転位を除去するための絞り工程でルツボ回転数を１ｒｐｍ以下に制限すると共に、水平方向に０．１テスラ以下の微弱磁場を印加し、且つ、絞り工程から増径工程に移行する段階でその磁場印加を停止することにより、絞り工程での径変動を安定的に抑制でき、増径工程での有転位化及び制御不能も回避できる。
【図面の簡単な説明】
【図１】本発明のシリコン単結晶成長方法の実施に適したＣＺ引上げ炉の縦断面図である。
【図２】ルツボ回転数の変更パターンを例示するグラフである。
【図３】ＣＺ法によるシリコン単結晶成長方法の説明図である。
【符号の説明】
１　ルツボ
２　ヒータ
５　引上げ軸
６　支持軸
７　チャンバ
１２　単結晶
１３　溶融液
１５　種結晶
３０　超電導磁石[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for growing a silicon single crystal using the CZ method (Czochralski method), and more particularly, to a method for growing a silicon single crystal in which a magnetic field is applied in order to prevent a change in crystal diameter in the drawing step.
[0002]
[Prior art]
There are various methods for manufacturing a silicon single crystal used for a semiconductor substrate, and a method used industrially is the CZ method, which is a rotary pulling method. In the production of a silicon single crystal by the CZ method, a crucible 1 arranged in a chamber is used as shown in FIG. The crucible 1 has a double structure in which a quartz crucible 1a containing a silicon melt 13 is held by a graphite crucible 1b from the outside, and is fixed on a support shaft 6 that can rotate and move up and down.
[0003]
In operation, first, the silicon raw material for crystal filled in the crucible 1 is melted in a predetermined atmosphere by a cylindrical resistance heating type heater 2 arranged substantially concentrically outside the crucible 1, and the molten liquid 13 is melted. Form. Next, the pulling shaft 5, which is disposed on the central axis of the crucible 1 and has the seed crystal 15 attached to the lower end, is lowered, and the seed crystal 15 is immersed in the melt 13. Then, while rotating the crucible 1 and the pulling shaft 5 in a predetermined direction at a predetermined speed, the pulling shaft 5 is pulled upward to grow the silicon single crystal 12 below the seed crystal 15.
[0004]
In such a CZ method, in order to remove dislocations originally contained in the seed crystal 15 and dislocations introduced by heat shock at the time of liquid contact, an operation of narrowing the seed crystal 15 to a diameter of about 3 mm after the liquid contact is performed. Is This is the drawing process. Thereafter, the crystal diameter is gradually increased and finally converged to the product diameter. As a result, a shoulder portion having a gradually increased diameter is formed below the thin narrowed portion, and a straight body portion having a constant diameter is formed below the shoulder portion. The step of gradually increasing the crystal diameter to form a shoulder is a diameter increasing step, and the step of forming a constant diameter straight body is a constant diameter step.
[0005]
The surface of a quartz crucible used for producing a silicon single crystal by the CZ method is melted by contact with a silicon melt, and oxygen is released into the melt. Part of the oxygen thus dissolved in the melt is taken into the silicon single crystal, and has various effects on the quality of the silicon single crystal. Therefore, in the CZ method, it is an important technical subject to control the amount of oxygen taken into the silicon single crystal.
[0006]
As one of the methods for controlling the oxygen concentration, there is a magnetic field applying CZ method called an MCZ (Magnetic-field-applied CZ) method. In this method, a magnetic field is applied to a melt in a quartz crucible to suppress and control convection in a direction perpendicular to the lines of magnetic force. There are various methods for applying a magnetic field, and among them, the HMCZ (Horizontal MCZ) method for applying a magnetic field in the horizontal direction has been put into practical use. The magnetic field strength used here is usually 0.3 to 0.4 Tesla.
[0007]
Meanwhile, as a recent trend, the diameter and weight of a single crystal to be grown are rapidly increasing, and at present, crystals having a diameter of 300 mm and a weight exceeding 200 kg are also produced. And the crystal weight tends to further increase. However, it is difficult to hold such a heavy crystal with the diameter (about 3 mm) of the drawn part in the drawing step of the ordinary CZ method. In addition, when the diameter of the constricted portion changes due to the liquid temperature fluctuation due to the convection of the melt, and as a result the diameter is partially reduced, it becomes more difficult to hold the heavy crystals.
[0008]
As means for solving such a problem of the diameter variation of the narrowed portion, a magnetic field in the narrowing process disclosed in Japanese Patent Application Laid-Open Nos. 10-7487, 9-165298 and 11-209197, etc. There is an application.
[0009]
More specifically, in Japanese Patent Application Laid-Open No. 10-7487, a magnetic field of 0.2 Tesla or less is applied in the drawing step in the MCZ method, and in the diameter increasing step following the drawing step, 0.2 mm is applied to the constant diameter step. It is described that the magnetic field is increased to a level exceeding Tesla.
[0010]
In Japanese Patent Application Laid-Open No. 9-165298, a magnetic field of 1.5 Tesla or more is applied in the drawing step in the normal CZ method, and in the diameter increasing step following the drawing step, the magnetic field is reduced to a magnetic field-free toward the constant diameter step. Has been described.
[0011]
Japanese Patent Application Laid-Open No. H11-209197 discloses that a magnetic field weaker than that of a constant diameter step is applied or a magnetic field is not applied in a drawing step and a diameter increasing step in the MCZ method. It is shown that a horizontal magnetic field is applied, the magnetic field is increased from 1 Tesla to 4 Tesla in a diameter increasing step, and a magnetic field of 4 Tesla is applied in a constant diameter step.
[0012]
[Problems to be solved by the invention]
As can be understood from the above, the application of a magnetic field in the drawing step is roughly classified into two methods, a method of increasing the magnetic field and a method of weakening the magnetic field by a magnetic field operation in the diameter increasing step following the drawing step. In any method, by applying a magnetic field in the drawing step, the convection of the melt is suppressed, and the diameter variation of the drawing part is suppressed.
[0013]
However, if the magnetic field is strengthened in the diameter increasing step following the drawing step, or if the magnetic field strength in the drawing step is maintained as it is, there is a problem that dislocations frequently occur in the diameter increasing step. The reason is considered as follows.
[0014]
When a magnetic field is applied to the silicon melt, as described in “Hiroshi Nogami: Proceedings of the 11th JSME Computational Mechanics Conference (1998) P414”, the magnetic field is applied in the direction of the magnetic field passing through the center of the crucible. A roll-shaped flow that is symmetric with respect to the parallel plane occurs. In a state where the temperature of the melt is relatively high as in the initial stage of the diameter increasing step, the flow is strong, and foreign substances existing in the melt are transported to the growth interface, and the dislocation is promoted.
[0015]
On the other hand, when the application of the magnetic field is stopped in the diameter increasing step as described in JP-A-9-165298, the above-mentioned convection in the form of a roll disappears, and foreign matter is transported to the growth interface by this convection, and Dislocations are prevented. However, on the other hand, it has been found that there is a danger that the temperature difference due to the convection change accompanying the demagnetization increases, and the crystal diameter rapidly increases, leading to loss of control.
[0016]
Also, in the drawing process in which a magnetic field is applied, depending on the number of rotations of the crucible, the temperature fluctuation of the melt becomes large due to the interaction between the melt and the crucible rotation that is stopped by the magnetic field. The problem that is not suppressed arises. This problem becomes remarkable when a large-diameter crystal having a diameter of 200 mm or more is pulled using a large-diameter crucible having a diameter of 700 mm or more.
[0017]
An object of the present invention is to provide a silicon single crystal growth method capable of stably suppressing a diameter variation in a drawing step and avoiding dislocations and uncontrollability in a diameter increasing step.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have studied in detail the effect of the application of a magnetic field on the formation of the constricted portion, and the effects of various factors other than the magnetic field. As a result, the following facts became clear.
[0019]
First, application of a magnetic field to the melt, particularly application of a magnetic field in the horizontal direction, is effective in suppressing the fluctuation of the diameter of the constricted portion. Secondly, in order to suppress dislocations in the diameter increasing step, which becomes a problem when a magnetic field is applied in the drawing step, it is essential to stop the magnetic field application in the diameter increasing step. Thirdly, it is effective to make the magnetic field applied in the drawing step as small as possible to reduce the physical change when demagnetizing in order to make the diameter control unstable due to demagnetization in the diameter increasing step. . Fourth, when the diameter variation of the narrowed portion is suppressed by applying a magnetic field, the rotation speed of the crucible is also an important factor in suppressing the diameter change, and it is necessary to keep the rotation speed as low as possible.
[0020]
The silicon single crystal growth method of the present invention has been completed on the basis of such knowledge, and is filled with a silicon material for crystal in a crucible, melted, and pulled up while rotating a seed crystal immersed in the melt. Accordingly, in the silicon single crystal growth method by the CZ method in which a silicon single crystal is grown below the seed crystal, the crucible rotation speed is set to 1 rpm or less in the drawing step for removing dislocations, and 0.1 tesla in the horizontal direction. The following magnetic field is applied, and the application of the magnetic field is stopped at the stage of shifting from the drawing process to the diameter increasing process.
[0021]
In order to suppress the fluctuation of the diameter of the constricted portion, it is effective to suppress the convection of the melt by applying a horizontal magnetic field. However, when a magnetic field exceeding 0.1 Tesla is used, when the application of the magnetic field is stopped, the temperature difference accompanying the change in convection increases, and the crystal diameter rapidly increases, resulting in loss of control. Therefore, the magnetic field intensity used in the drawing step is set to 0.1 Tesla or less, and particularly preferably 0.08 Tesla or less. It should be noted that a weak magnetic field of about 0.03 Tesla is sufficiently effective to suppress the convection of the melt, which is the main cause of the diameter fluctuation of the throttle portion. In this respect, the lower limit of the magnetic field strength is preferably equal to or greater than 0.01 Tesla, and particularly preferably equal to or greater than 0.03 Tesla.
[0022]
When the application of a magnetic field in the drawing process is applied to pulling a large single crystal with a large diameter using a large-diameter crucible, if the crucible rotation speed in the drawing process is large, the interaction between the melt and the crucible rotation stopped by the magnetic field As a result, the temperature fluctuation of the melt becomes large, and despite the application of a magnetic field, the diameter of the narrowed portion becomes large due to the opposite effect, making it difficult to hold a heavy crystal. For this reason, the crucible rotation speed in the drawing step is set to 1 rpm or less under the application of a magnetic field. The lower limit of the crucible rotation speed is not particularly limited, and the crucible rotation need only be stopped. From the viewpoint of maintaining the stable rotation of the crucible, the rotation speed is preferably 0.2 rpm or more from the viewpoint of device accuracy.
[0023]
After the magnetic field is stopped, if the diameter increasing step is performed while maintaining such a low crucible rotation, natural convection from the outer periphery to the center in the crucible occurs, and dislocations are formed in order to transport foreign matter to the growth interface. It is easy to occur. To solve this problem, it is effective to increase the number of rotations of the crucible, and to prevent the foreign matter from being transported by centrifugal force and accompanying forced convection. Specifically, it is preferable to change the crucible rotation speed to 3 rpm or more during the diameter increasing step until the crystal diameter reaches 100 mm.
[0024]
As described above, a stable drawing process and a diameter increasing process can be performed, and a magnetic field is applied again at the time of shifting from the diameter increasing process to the constant diameter process, and the crucible rotation speed is changed to a predetermined rotation speed, thereby increasing the weight. HMCZ method is also possible. The magnetic field strength in the constant diameter step is preferably 0.1 to 0.4 Tesla, and the crucible rotation speed is preferably 0.2 to 10 rpm.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a CZ pulling furnace suitable for carrying out the silicon single crystal growth method of the present invention, and FIG. 2 is a graph illustrating a change pattern of a crucible rotation speed.
[0026]
First, the structure of the CZ pulling furnace used in the silicon single crystal growth method of the present embodiment will be described.
[0027]
The present CZ pulling furnace includes a cylindrical main chamber 7a and a small-diameter pull chamber 7b mounted on the main chamber 7a as a chamber 7, which is a furnace body.
[0028]
The crucible 1 is arranged in the center of the main chamber 7a. The crucible 1 has a double structure in which a quartz crucible 1a containing a silicon melt 13 is held by a graphite crucible 1b from the outside, and is fixed on a support shaft 6 that can rotate and move up and down.
[0029]
Outside the crucible 1, a cylindrical resistance heating type heater 2 is disposed substantially concentrically. Further outside the heater 2, a cylindrical heat retaining cylinder 8 a is arranged along the inner surface of the main chamber 7 a. A heat retaining plate 8b is disposed on the bottom of the main chamber 7a.
[0030]
On the central axis of the crucible 1, a wire serving as the pull-up shaft 5 is suspended concentrically through a pull chamber 7b. The pulling shaft 5 holds a seed crystal 15 at the lower end, and is driven to rotate and vertically by a winding mechanism provided at the uppermost part of the pull chamber 7b.
[0031]
On the other hand, outside the main chamber 7a, a pair of superconducting magnets 30a and 30b are arranged to face each other to apply a horizontal magnetic field to the melt 13 in the crucible 1.
[0032]
Next, a method of growing a silicon single crystal 12 having a diameter of 300 mm using such a pulling furnace will be described.
[0033]
A crucible 1 filled with 300 kg of a silicon material for crystallization and added with phosphorus as an impurity is set in the chamber 7. The diameter of the quartz crucible 1a is 750 mm. The pressure in the chamber 7 is reduced to 25 Torr, and Ar gas at 100 L / min is introduced as an inert gas. The crystal silicon raw material and phosphorus in the crucible 1 are heated and melted by the heater 2 to form a melt 13.
[0034]
After the melt 13 is formed, a horizontal magnetic field of 0.05 Tesla is applied to the melt 13 by the superconducting magnets 30a and 30b, and after the melt temperature is stabilized, the seed crystal 15 is immersed in the melt 13; While rotating the crucible 1 and the pulling shaft 5 in a predetermined direction at a predetermined speed, the pulling shaft 5 was pulled upward to reduce the crystal diameter from 15 mm to 5 mm. In this drawing step, the rotation speed of the crucible 1 was 1.0 rpm, and the rotation speed of the pulling shaft 5 was 10 rpm. The magnetic field strength was maintained at 0.05 Tesla.
[0035]
Immediately after the drawing step, the application of the magnetic field was stopped, and the process was shifted to the diameter increasing step. In the diameter increasing step, the crucible rotation speed was increased as the crystal diameter increased so that the crucible rotation speed became 5 rpm when the crystal diameter became 100 mm. Thereafter, the crystal diameter was increased to 310 mm while maintaining the crucible rotation speed at 5 rpm, and the increased diameter portion (shoulder portion) 12a was completed.
[0036]
Then, when the crystal diameter reached 310 mm, the process was shifted to the constant diameter process, and a straight body portion 12b having a length of 1400 mm was grown. The total weight of the grown single crystal 12 is 270 kg. By reducing the applied magnetic field strength in the drawing step to 0.1 Tesla or less, reducing the crucible rotation speed to 1 rpm or less, and demagnetizing in the diameter increasing step, the fluctuation in the diameter of the drawing part is slightly suppressed, which is the target value. While 5 mm was maintained over almost the entire length, stable diameter control was continued even in the diameter increasing step, and as a result, stable pulling was performed. The crystal quality was also good.
[0037]
As another embodiment, the same process as in the previous embodiment is performed up to the diameter increasing step. When the crystal diameter reaches 300 mm, a horizontal magnetic field of 0.03 Tesla is applied, and the crucible rotation speed is reduced from 5 rpm to 1 rpm. changed. Then, a 1400 mm straight body was grown. Of course, stable pulling was performed, and there was no problem with DF characteristics and quality.
[0038]
For comparison, a tensile test was performed on a drawn portion formed by a normal CZ method (no magnetic field). It turned out that it could not be raised.
[0039]
[Table 1]

[0040]
Also, even if a magnetic field is applied in the drawing step, if the strength exceeds 0.1 Tesla, for example, 0.3 Tesla, the crystal diameter is reduced despite the stop of the magnetic field application at the time of shifting to the diameter increasing step. Dislocation occurred before reaching 100 mm. The crucible rotation speed was the pattern shown in FIG.
[0041]
Further, even if the magnetic field intensity applied in the drawing step is 0.1 Tesla or less, for example, 0.05 Tesla, and the application of the magnetic field is stopped at the time of shifting to the diameter increasing step, the number of crucible rotations in the drawing step is reduced. Is more than 1 rpm, for example, 3 rpm, the diameter variation in the drawing process becomes large, and it becomes difficult to hold a heavy crystal.
[0042]
Further, even when the intensity of the magnetic field applied in the drawing step is 0.1 Tesla or less, for example, 0.05 Tesla, and the crucible rotation speed in the drawing step is 1.0 rpm, the application of the magnetic field is continued in the diameter increasing step. When it was performed, dislocations occurred frequently in the early stage of the diameter increasing step. The crucible rotation speed was the pattern shown in FIG.
[0043]
【The invention's effect】
As described above, the silicon single crystal growth method of the present invention limits the crucible rotation speed to 1 rpm or less and applies a weak magnetic field of 0.1 Tesla or less in the horizontal direction in the drawing step for removing dislocations. In addition, by stopping the application of the magnetic field at the stage of shifting from the drawing process to the diameter increasing process, it is possible to stably suppress the diameter variation in the drawing process, and to avoid dislocations and uncontrollability in the diameter increasing process. .
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a CZ pulling furnace suitable for carrying out a silicon single crystal growth method of the present invention.
FIG. 2 is a graph illustrating a change pattern of a crucible rotation speed;
FIG. 3 is an explanatory diagram of a silicon single crystal growth method by the CZ method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Crucible 2 Heater 5 Pull-up shaft 6 Support shaft 7 Chamber 12 Single crystal 13 Melt 15 Seed crystal 30 Superconducting magnet

Claims (4)

A silicon single crystal growth method by a CZ method in which a silicon material for crystal is filled in a crucible and melted, and a seed crystal immersed in the melt is pulled up while rotating, thereby growing a silicon single crystal below the seed crystal. In the drawing step for removing dislocations, the crucible rotation speed is set to 1 rpm or less, and a magnetic field of 0.1 Tesla or less is applied in the horizontal direction, and the magnetic field is applied at the stage of shifting from the drawing step to the diameter increasing step. A method for growing a silicon single crystal, comprising: stopping. 2. The silicon single crystal growth method according to claim 1, wherein the crucible rotation speed is changed to 3 rpm or more when the crystal diameter is 100 mm or less during the diameter increasing step. 3. The method of growing a silicon single crystal according to claim 1, wherein a magnetic field is applied again during the transition from the diameter increasing step to the constant diameter step to change the crucible rotation speed to a predetermined rotation speed. 4. The method of growing a silicon single crystal according to claim 1, wherein a large diameter crystal having a diameter of 200 mm or more is pulled up using a large diameter crucible having a diameter of 700 mm or more.

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